The research described nthis application encompasses several studiesof two major diseases entities, i.e., (1) Crohn's disease and (2) cancer of the colon. These studies include (1) a retrospective study of risk factors (including use of oral contracetives and replacement estrogens) for Crohn's disease in women, (2) a cohort study of the association between Vitamin D status and incidence of cancer of the colon, (3) a cohort study of the association between consumption of milk and cancer of the colon, and (4) a retrospective study of high density lipoproteins and colon cancer. The study of (4) a retrospective study of high density lipoproteins and colon cancer. The study of Crohn's disease is designed to determine is use of oral contraceptives or replacement estrogens confers an excess risk of Crohn's disease, after controlling for age, smoking, religion, and other risk factors. The cohort study of Vitamin D and colon cancer was stimulation by an observed correlation between annual levels of sunlight intensity and mortality rates of cancer of the colon, in conjunction with suggestions of a protective effect of milk (most of which is fortified with Vitamin D) against cancer of the colon in a retrospective study of Seventh-Day Adventists in California, and a prospective study of Western Electric Company Employees in Chicago, Illinois. This study will be performed using samples of sera collected in 1974 (and forzen at -70 C) from 27,000 residents of Washington County, Maryland. The study of milk comsumption and cancer of the colon was also stimulated by the results of previous studies. It will be carried out in collaborationwith colleagues at the University of California, San Diego, using results from a questionnaire completed in 1973-74 by 6,087 residents of Rancho Bernardo, CA, a retirement community. The retrospective study of high density lipoproteins (HDL), cholesterol, and cancer was stimulated by current controversy in the epidemiologic literature regarding the effects of these factors on cancer of the colon, and will be carried out in collaboration with colleagues at the University of California, San Diego. Ambulatory cases of colon cancer, studied before surgery, radiation therapy, or chemotherapy, will be compared with healthy controls in terms of HDL and serum cholesterol levels, with the factors such as smoking, physical activity, nd obesity controlled in the analysis.